I'm sorry, that was not a service plumber.
He was looking for something he could wrap his brain around.
It's common for tub leaks to be caused by the upper rubber washer around the tub overflow.
That normally happens only if you have someone taking baths with an overflowing tub. Women take more baths like that, guys tend to shower more.
But if you stand just so, water can splash off the back and still hit the overflow and leak through.
Remove the screw and check it yourself. Hardware stores carry the replacement foam washers.